The ethanol extract of Rhodomyrtus tomentosa (Aiton) Hassk. (R. tomentosa) was determined for its antibacterial activity on staphylococci isolated from acne lesions. Antibiotic susceptibility patterns of the isolates were performed. Preliminary screening of the antibacterial property of the extract using disk diffusion method demonstrated pronounced antibacterial activity of the extract on all tested isolates. The average inhibition zones of 64 coagulase-positive and 85 coagulase-negative isolates were 12 mm and 14 mm, respectively. Minimal inhibitory concentration (MIC) was determined by broth microdilution method. The MIC50 and MIC90 ranged from 64-512 μg/ml. Time-kill curves were assessed at 0.5 MIC, MIC, 2 MIC, and 4 MIC by counting viable bacterial cells after time intervals. At 4 MIC, the level of treated staphylococci declined by at least 3 log fold within 6-8 hr. Rhodomyrtone, a pure compound in acylphloroglucinol class, isolated from this plant species was very effective against Staphylococcus aureus (S. aureus) ATCC 25923 with the MIC value at 0.5 μg/ml which is very closed to that of vancomycin. This finding challenges the use of rhodomyrtone as an alternative agent for staphylococcal cutaneous infections.
2008 by The Pharmaceutical Society of Japan